Dinosaurs rose from obscurity after the Permian catastrophe

Brusatte traces dinosaur origins to the aftermath of the end-Permian mass extinction roughly 252 million years ago, the most severe extinction event in Earth's history, which wiped out the vast majority of species and left ecosystems open for new groups to fill vacated niches. Early dinosaurs that emerged in the following Triassic period were small, unremarkable reptiles, overshadowed by other groups like the crocodile-relatives that initially dominated many terrestrial ecosystems. Brusatte emphasizes that dinosaurs' eventual dominance was neither immediate nor guaranteed; for millions of years they remained a minor part of the landscape, competing against better-established reptilian lineages. Their breakthrough came gradually, aided by another extinction event at the end of the Triassic that eliminated many of their competitors, allowing dinosaurs to expand rapidly into the ecological space left behind. This slow, contingent rise complicates any narrative of dinosaurs as an inevitably destined dominant group, framing their eventual empire instead as the product of surviving successive winnowing events better than their rivals did. Takeaway: dinosaur dominance was earned gradually, not preordained.